1. Field of the Invention
The present invention relates to an information processing apparatus for performing three-dimensional measurement on a measurement target object, and an information processing method.
2. Description of the Related Art
For measurement of a shape, a position, and an orientation of an object to be measured in a three-dimensional space, a measurement apparatus for measuring depth information of a surface of the object to be measured with respect to an imaging apparatus has been provided. Especially, in a non-contact type measurement apparatus, methods for measuring depth information to a measurement target by analyzing reflected light of light emitted onto the measurement target are widely used.
The measuring methods include, for example, a light-section method and a spatial coding method in which an imaging apparatus (camera) captures an image of a measurement target onto which known structured light is projected, and depth information is calculated using a trigonometric method from the light source position, the camera position, and the pattern position on the captured image. Further, the methods for calculating the position and orientation of the measurement target often uses a method for fitting a shape model of the measurement target to depth information or a two-dimensional image.
A position and orientation measurement method by model fitting is discussed in a document 1, P. J. Besl and N. D. Mckay, “A Method for Registration of 3-D Shapes”, IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 14, No. 2, pp. 239-256, 1992. In the method discussed in the document 1, the position and orientation of an object are estimated by performing nearest neighbor search on correspondence of measurement points acquired from depth information and a shape model surface, and minimizing the corresponding distances.
However, when a user acquires the depth information (three-dimensional position) of the measurement target according to the above-described conventional method, the acquirement accuracy of the depth information may decrease depending on various conditions.
For example, it is assumed that a receiving unit receives reflected light of structured light projected onto a measurement target, and the depth information is measured using a trigonometric method. In such a case, if the target object is a semi-transparent object made of a material containing plastic or wax, the light scatters in the target object (i.e., subsurface scattering). Due to the subsurface scattering, the projection light is measured at a position deviating from the projection position. As a result, the distance value different from a true distance value is measured.
In another case, if the measurement target object is a material which causes anisotropic reflection such as mica, metal, shiny fiber, or the like, the accuracy in the depth information acquisition may be decreased due to the anisotropic reflection. Further, depending on the calibration accuracy of a camera (imaging apparatus), the depth information acquisition accuracy may decrease.
To deal with the subsurface scattering, a method is discussed in the document 2, M. Gupta, Y. Tian, S. G. Narasimhan, and L. Zhang, “(De) Focusing on Global Light Transport for Active Scene Recovery”, IEEE Computer Vision and Pattern Recognition (CVPR) 2009. In the method, using a phenomenon in which a high-frequency pattern is attenuated due to subsurface scattering, a projection pattern in a phase shift method is converted into a high-frequency pattern.
By the method discussed in the document 2, a distance value can be measured while effects due to indirect reflection components such as the subsurface scattering are reduced. However, such a method takes time for the measurement because a plurality of times of projection of high-frequency patterns by shifting phases is required in addition to projection of a pattern minimum required to the distance measurement. Moreover, in the method discussed in the document 2, if an object to be measured may have a subsurface scattering characteristic, the object is measured using scatter components on the surface, so that the information of the subsurface scattering is not used.